Many drugs of abuse are known to disrupt learning and performance. Little is known, however, about the behavioral mechanisms that are affected when learning is disrupted. The focus of the present application is study the effects of drugs on human learning and performance by employing the repeated acquisition of behavioral chains procedure. This procedure has been productively employed in the animal laboratory but has been infrequently examined in humans. The procedure provides a method by which learning can be repeatedly studied in the same subject. Not only will this project obtain a profile of a variety of drugs on this procedure in humans but also later studies will try to identify the behavioral mechanisms (either stimulus control or reinforcement) which are affected by drugs. By identifying the behavioral mechanisms which are affected by drugs we increase our ability to generalize to other behavior similarly controlled. This project will also collect traditional clinical pharmacology measures of self-report as well as the effects of drug on physiology. By collecting these various types of measures, comparisons across them can be made. The studies will employ cumulative dosing procedure which will increase the efficiency of the study but also obtain dosing patterns that more closely approximates typical drug self-administration. The subjects will be tested again the day after cumulative dosing which will permit the assessment of residual drug effects ('hangover').